Gates mother introduced Microsoft to IBM for the contract by speaking with the then Chairman of IBM, who she was an acquaintance of. How many of your parents can do something like that?
Sure, Bill is a very smart person. But it's kind of impossible to say for sure whether he could have been as sucessful, if he was born in a different family. Parents play a major role in shaping the mind of children. For what we know Bill would not even have gone for a programming career and might have been a TV news reporter was he born in some other family.
If he is born in some other family, is he even Bill?